Anode for copper plating



United States te ANODE FOR COPPER PLATING Barnet D. Ostrow, North Bellmore, and Fred I. Nobel,

North Valley Stream, N. Y.

No Drawing. Application January 21, 1955, Serial No. 483,420

3 Claims. (Cl. 204-52) The present invention is directed to copper containing compositions, more particularly to copper anodes adapted to give improved results when used as anodes in alkaline cyanide copper electroplating baths.

In the plating of copper in the cyanide bath, and especially in the more recently adopted high'efiiciency type of bath, one of the most troublesome difficulties has been -the roughness of the deposited coating. This difiiculty becomes more pronounced as the thickness of the coat- 1 ing increases, and when the thickness is of the order of ..0005" and greater, the roughness has proven to be quite a problem with adverse effects on the corrosion resistance and the difficulty in bright nickel plating over the copper. Under many conditions inherent in commercial operation the roughness of the deposit begins to vappear at thicknesses of about .0002". cyanide copper electrolyte has been filtered so that it is Even when the crystal clear, there is still a great tendency of the bath to give roughness in the heavier deposits.

It has been proposed to overcome the roughness of the deposit, which is caused by poor anode corrosion and metallic particles detached from the anode, by providing a system of anode diaphragms. Although it has been recognized for some time that this type of roughness 'was due to conditions at the anode, attempts to overcome the difiiculties were confined to such mechanical means as diaphragms or to the use of copper electrodes of as 'high a purity as possible, which were not completely successful and which introduced complications.

The conventional type of copper anode presently used 'in the standard high efficiency cyanide copper baths is electrolytic copper sheet. The use of cast or rolled copper anodes is. disadvantageous, since such anodes reduce sludging and to prevent roughness of the deposit especially in the deposits of increased thickness. While such an anode has been found to operate successfully in acid copper plating baths, its use in alkaline cyanide copper; baths'does not overcome the difiiculties and is either worthless or even harmful, since it produces deposits which may be even rougher than when anodes substantially free from phosphorus are used.

In cyanide copper plating baths there is a marked tendency for poor anodic corrosion and the development of anodic passivity which interfere with the efficiency of the plating operation and contribute greatly to cathodic deposit roughness. It has been proposed to overcome this defect by increasing the amount of free cyanide in the electrolyte above the optimum of the bath. In the present day high speed bright copper plating processes,

t C "ice 2,809,929 Patented Oct. 15, 1957 basic advantages of the high efficiency plating. baths are lost.

Another proposal for overcoming the above described difiiculties in the alkaline cyanide copper plating process has been the use of forged ball type copper anodes. While such anodes have frequently given good results in reducing the roughness of the deposited metal, they are considerably. more costly thanthe conventional sheet, cast .or rolled anodes,-because of'the forging operations required in the fabricationthereof. The results obtained in eliminating roughness of deposits are erratic and-the difliculty of anodic polarization and passivity is not overcome.

The present invention is-intended and adapted to overcome the diflieultiesand" disadvantages inherent in prior high speed brightcopper'plating processesand baths, it

being among-the objects "ofthe invention "to provide a copper anode of a suitable-composition which will produce a uniform and smooth cathode deposit free from roughness. V,

It is also among the objects of the invention to provide an anode composition which has uniform corrosion, does not develop passivity and does not form sludge during the electroplating operation overlong periodsof time.

It isfurther among the objects of the invention to utilizean-anode'of the abovedescribed'type'in any of a variety of forms including electrolytic sheet, and rolled and cast metal.

The invention is based upon the discovery that all of the above noted undesirable characteristics of alkaline cyanide copper plating baths and the difficulties of anode passivity and roughness of deposit, are overcome by the provision of a copper anode containing small amounts and in controlled quantities of a metal of the ironvgroup, namely nickel, cobalt or iron, or a mixture of two or all three of these metals. The amount of the added metal varies from about .05% to 1.5% based on the copper. Lesser amounts do not have any substantial effectiveness and amounts greater than 1.5 do not give increased benefits and may even be harmful in some cases. It has been found that copper anodes containing from about 0.2% to 0.4% give the optimum results in the plating operation.

When" the copper "anode is substantially" free from oxygen," such asOFHC copper; excellent operating characteristi'cs'areinherentirithe' anodes. The anodes may be rendered"oxygemfreebytheuseofsilicon as a deoxidizer, in which case the amount of residual silicon should preferably not exceed about 204%. If phosphorus is used asthe deoxidizer the residual amount should preferably not exceed about .01%. It is de'sirablethatsuch residual amounts-be as low as practical. 'The presence of the additives of. the iron group alloyed with and uniformly distributed in the copper anodewhichis oxygen free has been found to eliminate practically. all of .the difficulties heretofore encountered.

The copper is quite 'pureexceptforrthe" presence 'o the above mentioned substances and the small amount of impurities normally present in commercial refined copper. The purer the copper, the better are the results obtained thereby.

With the anodes of the present invention it is possible to obtain a considerable improvement in the performance of the plating bath even if the deoxidizer is present in the anode in concentrations substantially higher than those stated above, although considerably better performance is obtained where the deoxidizer is present in the lower concentrations. For instance, in an anode containing 0.3% of nickel and having .0l% of residual phosphorus better performance is obtained than if the anode contained .03% of residual phosphorus. Residual silicon in an anode containing 0.3% of nickel gives better performance in the plating bath than a similar anode containing phosphorus. Still better performance is obtained the lower the concentration of the silicon present. Also the use of nickel in the anode has proven to be superior to the other metals of the iron group.

The following are specific examples of anode compositions included in the present invention:

The anodes of the present invention may be used in any of the usual commercial alkaline cyanide copper baths of which the following composition may be considered as typical:

Oz. Copper cyanide 3.5 Total sodium cyanide 5.0 Sodium carbonate 2.0 Free sodium cyanide 1.1 Rochelle salts 6.0

dissolved in one gallon of Water. The bath is usually operated at temperatures of about 135 F. to 175 F. and current densities from to 60 amperes per square foot are used.

A typical high efliciency bath is as follows:

Oz./ gal. Copper 8 Total KCN 12.7 KOH 5.0 Free KCN 1.5

Heavy deposits of copper electrolytically obtained from the above type of bath using the present anodes show a very marked reduction of roughness. The anode corrosion is uniform and excellent and the prior difiiculty of sludging has been substantially overcome. Passivity of the anode is practically eliminated. The coatings are uniform and smooth.

Copper anodes containing nickel have previously been described. They were intended to be used as coppernickel anodes for the electrolytic refining of the copper therein. However, such anodes contained large amounts of sulphur in the form of a matte having say 8 to 10% of sulphur together with relatively large percentages of nickel far above the amounts present in the present anodes. Such prior art anodes have no usefulness in the deposition of copper from alkaline cyanide baths, and the presence of sulphur in such prior anodes would foul the bath and make deposition of copper commercially impractical. Furthermore, the prior anodes contained a large amount of oxygen resulting from the treatment of the raw material by heat and oxygen to reduce the sulphur content down to 8 to 10%, which would render the anodes useless for the present purposes.

Although the invention has been described setting forth several specific examples thereof, the invention is not to be limited thereto as said examples are intended for the purpose of illustration only. Therefore, the invention is to be broadly construed and to be limited only by the character of the claims appended hereto.

We claim:

1. A method of electrolytically depositing copper from an alkaline cyanide copper bath which comprises carrying out said deposition by passage of an electric current from an anode of substantially pure copper containing only the small amount of impurities normally present in commercial refined copper, said anode having incorporated therein a metal taken from the class consisting of nickel, cobalt and iron in amount from about .05 to 1.5% based on said copper, through said alkaline cyanide copper bath to a cathode.

2. A method of electrolytically depositing copper from an alkaline cyanide copper bath which comprises carrying out said deposition by passage of an electric current from an anode of substantially pure copper containing only the small amount of impurities normally present in commercial refined copper, said anode having incorporated therein a metal taken from the class consisting of nickel, cobalt and iron in amount from about 0.2% to 0.4% based on said copper, through said alkaline cyanide copper bath to a cathode.

3. A method of electrolytically depositing copper from an alkaline cyanide copper bath which comprises carrying out said deposition by passage of an electric current from an anode of substantially pure copper containing only the small amount of impurities normally present in commercial refined copper, said anode being substantially free from oxygen and having incorporated therein a metal taken from the class consisting of nickel, cobalt and iron in amount from about .05 to 1.5 based on said copper, through said alkaline cyanide copper bath to a cathode.

References Cited in the file of this patent UNITED STATES PATENTS 1,510,541 Burdick Oct. 7, 1924 1,778,668 Fuller Oct. 14, 1930 2,086,841 Bagley et al. July 13, 1937 2,142,672 Hensel et al. Jan. 3, 1939 00 2,689,216 Nevers et al. Sept. 14, 1954 OTHER REFERENCES Nevers et al.: Plating, vol. 41 (1954), p. 1303.

Langes Handbook of Chemistry, fifth edition, 1944, p. 766. 

1. A METHOD OF ELECTROLYTICALLY DEPOSITING COPPER FROM AN ALKALINE CYANIDE COPPER BATH WHICH COMPRISES CARRYING OUT SAID DEPOSITION BY PASSAGE OF AN ELECTRIC CURRENT FROM AN ANODE OF SUBSTANTIALLY PURE COPPER CONTAINING ONLY THE SMALL AMOUNT OF IMPURITIES NORMALLY PRESENT IN COMMERCIAL REFINED COPPER, SAID ANODE HAVING INCOPORATED THEREIN A METAL TAKEN FROM THE CLASS CONSISTING OF NICKEL, COBALT AND IRON IN AMOUNT FROM ABOUT .05% TO 1.5% BASED ON SAID COPPER, THROUGH SAID ALKALINE CYANIDE COPPER BATH TO A CATHODE. 